| Project/Area Number |
14570010
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
General anatomy (including Histology/Embryology)
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| Research Institution | Shiga University of Medical Science |
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Principal Investigator |
NAKAMURA Takaaki Shiga University of Medical Silence, Medicine, Assistant Professor, 医学部, 助手 (30314157)
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| Co-Investigator(Kenkyū-buntansha) |
KASHIWAGI Atsunori Shiga University of Medical Silence, Medicine, Professor, 教授 (20127210)
KUDO Motoi Shiga University of Medical Silence, Medicine, Professor, 教授 (80108141)
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| Project Period (FY) |
2002 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 2003: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2002: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Keywords | transcription factor / sumovlation / iRNAs / diabetes mellitus / Pdxl / insulin / post-translation / NFk-B / 小腸幹細胞 / インスリン / Pdx1 / SUMO-1 / 過酸化物質 / β細胞死 / 膵β細胞 / 転写調節因子 / 再生 |
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| Research Abstract |
Pancreatic duodenal homeobox-1(Pdxl) is a transcription factor and its phosphorylation is thought to be essential for activation of insulin gene expression. This phosphorylation is related to concomitant shift in molecular mass from 31 to 46 kDa. However, we found that Pdxl was modified by SUMO-1 (small ubiquitin-related modifier 1) in beta TC-6 cells and COS-7 cells, which were transfected with Pdx-1 cDNA. This modification contributed to the increase in molecular mass of Pdxl from 31 to 46 kDa. Additionally, sumoylated Pdxl localized in nucleus. The reduction of SUMO-iRNA protein by use of RNA interference (SUMO-iRNA) resulted in a significant decrease in Pdxl protein in the nucleus. A 34-kDa form of Pdxl was detected by the cells exposed to SUMO-iRNAs in the presence of lactacystin, a proteosome inhibitor.
Furthermore, the reduced nuclear sumoylated Pdxl content was associated with significant lower transcriptional activity of insulin gene. Thesse findings indicated that SUMO-1 modif
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ication is associated with both the localization and stability of Pdx l as well as its effect on insulin gene activation.
Next, to clarify the effect of dietary lipid hydroperoxide (LPO) on development of glucose intolerance, we fed Sprague-Dawley rats on a diet containing elevated LPO level for 10 weeks and measured both insulin sensitivity and insulin secretion. The contents of LPO in both plasma and skeletal muscle in the LPO-fed rats were significantly higher than those in the controls. Both insulin resistance evaluated by steady-state blood glucose (SSBG) methods and impaired insulin secretion evaluated by oral glucose tolerance test (OGTT) were found in the LPO-fed rats as compared with control rats. Furthermore, the levels of insulin receptor substrate (IRS)-1 protein in the skeletal muscle were significantly lower in the LPO-fed rats. Those impairments were not reversed in LPO-fed rats with supernormal levels of plasma vitamin E following vitamin E supplementation for 5 weeks. Moreover, the immunohistochemical study revealed that NF-kB-p50 protein was found in the nucleus of pancreatic b-cells of the LPO-fed rats, whereas it was not observed in the nucleus of the islets in the control rats. These findings indicate that NF-kB is activated in response to oxidative stress in pancreatic islet cells in LPO-fed rats. In conclusion, our studies reveal that diet high in LPO by vitamin E-deficiency accelerates glucose intolerance through impairments of both sensitivity and secretion of insulin. Less
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